The present invention relates to an image forming method for developing an electrostatic latent image into a visible image by means of a developing agent and transferring the visible image to a recording medium.
The image forming method of this type is applied to electronic copying machines, facsimiles, electrostatic printing machines and various other apparatuses. This image forming method comprises steps of forming an electrostatic latent image corresponding to an image on the surface of a photosensitive drum including a photoconductive member, electrostatically applying a developing agent of resin or other material to the electrostatic latent image to develop it into a visible image (developing step), transferring the developing agent forming the visible image to a recording medium such as paper (transferring step), fixing the transferred image to the recording medium for image recording (fixing step), and removing the developing agent remaining on the photosensitive drum (cleaning step).
However, after these steps are repeated for thousands of image forming cycles, the developing agent would stick fast to the surface of the photosensitive drum to form black or colored spots thereon, despite the effect of the cleaning step. Owing to the production of the spots, the conventional image forming method is subject to the following drawbacks:
(A) The spots are also recorded on the recording medium to greatly lower the image quality;
(B) The spots make the surface of the photosensitive drum rugged, and the developing agent near the spots cannot thoroughly be removed, lowering the cleaning efficiency;
(C) A cleaning member suffers local abrasion attributed to contact with the spots which make the surface of the photosensitive drum rugged, and therefore shortens its life;
(D) Production of the spots in a short time shortens the replacement cycle for the photosensitive drum; and
(E) Frequent checking for the production of the spots and continual removal of the spots are required, thus increasing the maintenance cost.
The spots are produced when the developing agent initially attracted as a nucleus to the surface of the photosensitive drum grows and sticks fast thereto by the repetition of the image forming steps, or when the developing agent penetrates into the photosensitive drum through scratches or other flaws thereon. In any case, the production of the spots would be caused by the pressure or frictional heat which should be applied to the developing agent during the developing, transferring and cleaning steps.